There are two terms associated with fires the fire

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There are two terms associated with fires, the fire point and the flash point. (c) UPES, Not for Reproduction/ Sale
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UNIT 7: Aircraft Rescue and Fire Fighting Services Notes ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ The fire point of a substance is the lowest temperature at which its vapours can be ignited and would continue to burn. At this temperature, the vapour would ignite spontaneously in the air. Also, substances don't have to be heated to this ignition temperature throughout in order to ignite. The flash point of a substance is the temperature at which the substance gives off enough vapours to form an ignitable mixture with the air near the substance's surface. An ignitable mixture is a mixture within the explosive range. The mixture is capable of spreading a flame away from the source of ignition when ignited. For example, fuel would spontaneously ignite when a portion of it (or its vapours) is exposed to temperatures around 268°C (ignition temperature). It is capable of being touched off by a match or spark at temperatures down to –20°C (fire point). It would also flash across the surface at temperatures from –20°C down to –43°C (flash point). From these examples, it can be readily seen that fuel has a low flash point and is easily ignited. Fuel is a constant fire hazard around aircraft. A spark, heat caused by friction, or an electrical discharge could supply enough heat to cause fuel to flash. Classes of Fire Different types of fires are combated by different means. It is important for a fire person to identify various types of fires and to understand specific ways of combating each type of fire. Class A of Fire Class A fires occur in combustible materials, such as bedding, mattresses, books, cloth, and any matter that produces an ash. All fires of this class leave embers, which are likely to rekindle if air comes in contact with them. Class A fires must not be considered extinguished until the entire mass has been cooled below its ignition temperature. Smothering (removing the oxygen) is not effective for class A fires because it does not lower the temperature of the smouldering embers below the surface. The extinguishing agents most effective for class A fires are solid water stream, both high- and low-velocity fog, CO 2 , and water immersion. (c) UPES, Not for Reproduction/ Sale
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Notes ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ Aviation Safety & Security Management Class B of Fire Figure 7.3: Class B (Most Important from Aircraft Fire Point of View) Class B fires (shown in Figure 7.3) occur with flammable liquid substances. Examples of class B fires are gasoline, jet fuels, paints, grease, and any petroleum-based product. These and other combustible substances do not leave embers or ashes. Class B fires are extinguished by providing a barrier between the burning substance and oxygen necessary for combustion. Chemical and mechanical foams produce such a barrier and are known as permanent smothering agents, but their effect is only temporary. The application must be renewed if there is any danger of re-ignition. The extinguishing agents recommended for combating class B fires are CO 2 , PKP, Halon, and Aqueous Film-Forming Foam (AFFF). However, water by itself is
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  • Fall '19
  • Instrument approach, Runway, Rajiv, Aviation Safety & Security Management

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